1. Field of the Invention
The present invention relates to the field of displaying technology, and in particular to a color filter on array (COA) white organic light emitting diode (WOLED) structure and a manufacturing method thereof.
2. The Related Arts
OLED is a flat panel displaying technique of extremely prosperous future and it shows excellent displaying performance and possesses various advantages, such as being self-luminous, simple structure, being ultra-thin, fast response, wide view angle, low power consumption, and being capable of achieving flexible displaying and is thus regarded as a “dream display”. In addition, the investment of manufacturing installation is far less than that of TFT-LCDs (Thin-Film Transistor Liquid Crystal Displays) so that it is now favored by major display manufacturers and becomes the mainstream of the third-generation display devices in the field of displaying technology. Being on the eve of mass production, new techniques of OLED emerges virtually unlimitedly with the deepening of research and development thereof and thus, OLED displays are undergoing a break-through progress.
To achieve full colorization of OLED display devices, one way is achieved with superimposition of a WOLED and a color filter (CF). The superimposition of the WOLED and the CF allows for realization of high definition of the OLED display device without requiring precise and accurate masking operation.
A COA WOLED is a combination of the COA (CF on Array) technology and the WOLED technology. Using the COA technology allows a CF layer (red/green/blue photoresists) to be formed on an array substrate. And, white light emitting from a white light material of the OLED transmits through the red/green/blue photoresists to provide light of three primary colors of red, green, and blue. Compared to a conventional bottom emission OLED structure, such a technique does not suffer the constraint of being used to manufacture a large-sized panel as that of an organic evaporation mask so as to make it widely applicable to large-sized OLEDs.
FIG. 1 is a schematic view showing the structure of a red sub pixel zone of a conventional COA WOLED, which comprises a substrate 100, a gate terminal 200 formed on the substrate 10, a gate insulation layer 300 formed on the gate terminal 200, an island like oxide semiconductor layer 400 formed on the gate insulation layer 300, an island like etch stop layer 500 formed on the oxide semiconductor layer 400, source/drain terminals 600 formed on the etch stop layer 500, a passivation protection layer 700 formed on the source/drain terminals 600, a red photoresist layer 710 formed on the passivation protection layer 700, a planarization layer 800 formed on the passivation protection layer 700 and covering the red photoresist layer 710, an anode layer 101 formed on the planarization layer 800 and in contact engagement with the source/drain terminals 600 through a via 810, a pixel definition layer 110 formed on the anode layer 101, and a photo spacer 120 formed on the pixel definition layer 110. Structures of a green sub pixel zone and a blue sub pixel zone of the COA WOLED structure are similar to the red sub pixel zone.
One of the drawbacks of the above-described COA WOLED is the light emission efficiency of the three primary colors of red/green/blue is relatively low. A conventional top emission OLED device allows for adjustment of the thickness of the OLED device in order to make use of micro cavity resonance to effectively enhance the light emission efficiency. However, for the above-described COA WOLED, it is not possible to adjust the thickness of the device in the same way as the conventional OLED device in order to use the micro cavity effect to enhance the light emission efficiency of each color of light.